Optical fiber assemblies having a powder or powder blend at least partially mechanically attached

ABSTRACT

Disclosed are fiber optic assemblies having at least one optical fiber disposed within a tube and/or cavity along with a powder or powder blend that is at least partially mechanically attached thereto. In one embodiment, the powder or powder blend includes a water-swellable component that is mechanically attached to about 30 percent or less of the surface area of the tube wall while still effectively blocking the migration of water along the tube. Other embodiments may have the powder or power blend mechanically attached to the tube, cavity, or the like at relatively high percentage levels of the total powder or powder blend within the assembly, thereby inhibiting unintentional migration along the tube, cavity, or the like. Other embodiments may use powder or powder blends that may or may not include a water-swellable powder to provide other desired characteristics.

PRIORITY APPLICATION

This application is a continuation of U.S. patent application Ser. No.13/030,807 filed Feb. 18, 2011, now U.S. Pat. No. 8,180,190 which is acontinuation of U.S. patent application Ser. No. 12/221,118, filed Jul.31, 2008, now U.S. Pat. No. 7,916,989 the content of both are reliedupon and incorporated herein by reference in their entirety, and thebenefit of priority under 35 U.S.C §120 is hereby claimed.

FIELD OF THE INVENTION

The present invention relates generally to optical fiber assemblies usedfor transmitting optical signals. More particularly, the presentinvention relates to optical fiber assemblies including a powder or apowder blend for blocking water.

TECHNICAL BACKGROUND

Communications networks are used to transport a variety of signals suchas voice, video, data and the like. As communications applicationsrequired greater bandwidth, communication networks switched to cableshaving optical fibers since they are capable of transmitting anextremely large amount of bandwidth compared with a copper conductor.Moreover, a fiber optic cable is much smaller and lighter compared witha copper cable having the same bandwidth capacity.

In certain applications, fiber optic cables are exposed to moisture thatover time may enter the fiber optic cable. To address this moistureissue, fiber optic cables intended for these applications include one ormore components for blocking the migration of water along the fiberoptic cable. By way of example, conventional fiber optic cables blockwater migration using a filling and/or a flooding material such as gelor grease within the fiber optic cable. Filling material refers to gelor grease that is inside a tube or cavity with the optical fibers,whereas flooding material refers to gel or grease within the cable thatis outside of the cavity that houses the optical fibers. The gel orgrease works by filling the spaces (i.e., the voids) so that the waterdoes not have a path to follow within the fiber optic cable.Additionally, the gel or grease filling material has other advantagesbesides water blocking, such as cushioning and coupling of the opticalfibers which assists in maintaining optical performance duringmechanical or environmental events affecting the fiber optic cable.Simply stated, the gel or grease filling material is multi-functional.

However, gel or grease filling materials also have disadvantages. Forinstance, the gel or grease is messy and may drip from an end of thefiber optic cable. Another disadvantage is that the filling materialmust be cleaned from the optical fibers when being prepared for anoptical connection, which adds time and complexity for the craft.Moreover, cleaning the gel or grease requires the craft to carry thecleaning materials into the field for removing the gel or grease. Thus,there has been a long-felt need for fiber optic cables that eliminatethe gel or grease materials while still providing all of the benefitsassociated therewith.

Early fiber optic cable designs eliminated the flooding material byusing dry water-blocking components such as tapes or yarn outside thebuffer tubes for inhibiting the migration of water along the cable.Unlike the gel or grease, the dry water-blocking components are notmessy and do not leave a residue that requires cleaning. These drywater-blocking components typically include super absorbent polymers(SAPs) that absorb water and swell as a result, thereby blocking thewater path for inhibiting the migration of water along the fiber opticcable. Generally speaking, the water-swellable components used a yarn ortape as a carrier for the SAP. Since the water-swellable yarns and tapeswere first used outside the cavity housing the optical fibers, the otherfunctions besides water-blocking such as coupling and opticalattenuation did not need to be addressed.

Eventually, fiber optic cables used water-swellable yarns, tapes, orsuper-absorbent polymers (SAPs) within the tubes that housed the opticalfibers for replacing the gel or grease filling materials. Generallyspeaking, the water-swellable yarns or tapes had sufficientwater-blocking capabilities, but did not provide all of the functions ofthe gel or grease filling materials such as cushioning and coupling. Forinstance, the water-swellable tape and yarns are bulky since they arerelatively large compared with a typical optical fiber and/or can have arelatively rough surface. As a result, water-swellable yarns or tapesmay cause problems if the optical fiber is pressed against the opticalfibers. Likewise, the SAPs may cause problems if pressed against theoptical fibers. Stated another way, optical fibers pressed against theconventional water-swellable yarn, tapes, and/or SAPs may experiencemicrobending which can cause undesirable levels of optical attenuationand/or cause other issues. Moreover, the desired level of coupling forthe optical fibers with the tube may be an issue if the fiber opticcable is not a stranded design since the stranding provides coupling.

By way of example, U.S. Pat. No. 4,909,592 discloses conventional waterswellable components used within a buffer tube having optical fibers.But, including conventional water-swellable components within the buffertube can still cause issues with fiber optic cable performance thatrequires limitations on use and/or other design alterations. Forinstance, fiber optic cables using conventional water-swellable yarnswithin the buffer tube required larger buffer tubes to minimize theinteraction of conventional water swellable yarns and optical fibersand/or limiting the environment where the cable is used.

Other early fiber optic cable designs used tubes assemblies that werehighly-filled with SAPs as a loose powder for blocking the migration ofwater within the fiber optic cable. However, using a loose SAP powderwithin the fiber optic cable created problems since the SAPs powderscould accumulate/migrate at positions within the fiber optic cable sinceit was not attached to a carrier such as a yarn or tape (i.e., SAPspowders would accumulate at the low points when wound on a reel due togravity and/or vibration), thereby causing inconsistent water blockingwithin the fiber optic cable. Also, the loose SAP powder was free tofall out of the end of the tube. FIGS. 1 and 2 respectively depict across-sectional view and a longitudinal cross-sectional view of aconventional dry fiber optic assembly 10 having a plurality of opticalfibers 1 along with a loose water-swellable powder 3 as schematicallyrepresented disposed within a tube 5. As shown, conventional dry fiberoptic assembly 10 uses a relatively large quantity of SAP powder 3within tube 5 for blocking the migration of water therein. Otherconventional fiber optic cable components used embedded SAP powder inthe outer surface of a tube such as disclosed in U.S. Pat. No.5,388,175. However, embedding the SAP in the outer surfaces greatlyreduced the effectiveness of the same since water can not reached theparticles that are embedded.

The present invention addresses the long-felt need for dry fiber opticassemblies that provide suitable optical and mechanical performancewhile being acceptable to the craft.

SUMMARY OF THE INVENTION

The present invention is directed to dry fiber optic assemblies that usea powder or powder blend that is at least partially mechanicallyattached to a wall of the assembly. The fiber optic assemblies mayinclude one or more optical fibers and a powder or powder blend disposedwithin a tube, a cavity, a cable, or the like. Moreover, one or more ofthe fiber optic assemblies may be used in a cable or may itself form acable. For instance, the powder or powder blend may include awater-swellable powder for blocking the migration of water along theassembly for effectively blocking the migration of water. In otherembodiments, the powder or powder blend may have additional and/or othercharacteristics besides water-blocking such as flame-retardant or othersuitable characteristics.

It is to be understood that both the foregoing general description andthe following detailed description present embodiments of the invention,and are intended to provide an overview or framework for understandingthe nature and character of the invention as it is claimed. Theaccompanying drawings are included to provide a further understanding ofthe invention, and are incorporated into and constitute a part of thisspecification. The drawings illustrate various embodiments of theinvention and together with the description serve to explain theprincipals and operations of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of the conventional fiber opticassembly using a relatively large quantity of water-swellable powderloosely disposed therein for blocking the migration of water within thesame.

FIG. 2 is a longitudinal cross-sectional view of the conventional fiberoptic assembly of FIG. 1.

FIGS. 3 and 3A are cross-sectional views of fiber optic assemblieshaving a water-swellable powder for blocking the migration of wateraccording to different embodiments.

FIG. 4 is a greatly enlarged longitudinal cross-sectional view of thefiber optic assembly of FIG. 3.

FIG. 5 is a photograph showing a magnified view of the inner wall of atube having powder mechanically attached thereto with a region ofinterest depicted by a boxed area.

FIG. 5 a is the photograph of FIG. 5 with the powder identified using asoftware package to determine the percentage of surface area of theregion of interest that has the powder mechanically attached thereto.

FIG. 6 is a cross-sectional view of a fiber optic cable using the fiberoptic assembly of FIG. 3 in a stranded loose tube cable.

FIG. 7 is a cross-sectional view of another fiber optic cable accordingto another embodiment.

FIG. 8 is a cross-sectional view of another fiber optic cable accordingto the present invention.

FIG. 9 is a cross-sectional view of another fiber optic cable accordingto the present invention.

FIG. 10 is a cross-sectional view of another fiber optic cable accordingto the present invention.

FIG. 11 is a cross-sectional view of another fiber optic cable accordingto the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments disclosed have several advantages compared withconventional dry fiber optic assemblies that use water-swellable powder.One advantage is that fiber optic assemblies have at least a portion ofthe water-swellable powder or powder blend mechanically attached to asurface of the fiber optic assembly (i.e., the tube or cavity wall) overless than all of the surface area while still effectively blocking themigration of water. Moreover, the existence of water-swellable powderwithin the fiber optic assembly or cable is nearly transparent to thecraft since it is mechanically attached and may use relativelylow-levels. Additionally, no cleaning of the optical fibers is necessarybefore connectorization like with gel or grease and no components suchas water-swellable tapes or yarns require removing or cutting. Anotheradvantage of having at least some of the powder or powder blendmechanically attached to the inside surface of the tube, cavity or thelike is that it does not migrate like a loose powder of conventional dryfiber optic assemblies. Additionally, the tubes or cavities of the fiberoptic assemblies can have smaller dimensions than conventional dry cableassemblies that use tapes or yarns as the carrier. As used herein, fiberoptic assemblies include tube assemblies that exclude strength members,tubes assemblies having strength members, fiber optic cables, and thelike.

Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings. Whenever possible, the same reference numeralswill be used throughout the drawings to refer to the same or like parts.FIGS. 3 and 4 respectively schematically depict a cross-sectional and anenlarged longitudinal cross-sectional view of a fiber optic assembly 100(i.e., a tube assembly) according to a first embodiment. Fiber opticassembly 100 includes a plurality of optical fibers 102, and awater-swellable powder or powder blend 104, and a tube 106. Opticalfibers 102 may be any suitable type of optical waveguide as known orlater developed. Moreover, the optical fibers may be a portion of afiber optic ribbon, a bundle of optical fiber or the like. Optionally,optical fibers 102 are colored by an outer layer of ink (not visible)for identification and are loosely disposed within tube 106. In otherwords, optical fibers 102 are non-buffered, but the concepts of thepresent invention may be used with optical fibers having otherconfigurations such as buffered, ribbonized, stranded, etc. In stillfurther embodiments, the concepts disclosed herein may be used withhollow filler rods that do not include optical fibers therein. As shown,water-swellable powder 104 is, generally speaking, represented asdisposed about the inner surface of tube 106 with a portion thereofmechanically attached as discussed herein. Further, water-swellablepowder 104 is mechanically attached to a relatively small percentage ofa surface area of the tube inner wall so that its use in the fiber opticassembly 100 is nearly transparent to the craft, but is surprisinglyeffective since it provides adequate water-blocking performance.Additionally, fiber optic assembly 100 need not include anothercomponent for blocking the migration of water within tube 106, but itmay include other cable components.

Unlike conventional fiber optic tube assemblies, fiber optic tubeassemblies have relatively high-levels of water-swellable powder 104mechanically attached while still being able to block a one-meterpressure head of tap water within a one meter length for twenty-fourhours. As used herein, tap water is defined as water having a salinelevel of 1% or less by weight. Similarly, fiber optic tube assembliesdisclosed may also block saline solutions up to 3% by weight within 3meters for 24 hours, and the blocking performance may even stop the 3%saline solution within about 1 meter for 24 hours depending on thedesign. Mechanical attachment of the powder preferably allows a portionof the water-swellable particle to protrude beyond the surface so thatif water enters the cavity it may contact the particle. It is theorizedthat after the water contacts the water-swellable particle and initiatesswelling that some of the particles break free of the surface so theycan fully swell and/or move to form a water-blocking plug with otherparticles. In other words, if the particles of the powder remainattached to the surface or are embedded therein as in conventionaldesigns they can not fully swell and will not be effective since theycan not conglomerate with other particles. Thus, when mechanicallyattached the particles should have a portion thereof that protrudesbeyond the surface and not be completely embedded therein. It shouldalso be understood that not all of the water-swellable powder or powderblend is mechanically attached to the surface, but there may be someloose powder.

By way of example, water-swellable powder 104 is disposed within a tubehaving an inner wall with a given surface area per meter length. In oneembodiment, about 30 percent or less of the surface area of the innerwall of the tube has water-swellable powder and/or powder blendsmechanically attached thereto, but other percentages are possible suchas 25 percent or less. Moreover, the mechanical attachment may begenerally uniformly disposed on the surface area such as 30 percent orless of the entire surface as depicted. Conversely, mechanicalattachment may be concentrated in longitudinal stripes or the like suchas 100 percent or less mechanical attachment in one or more stripes thatcover 30 percent or less of the surface area and 0% mechanicalattachment at other locations as shown schematically in FIG. 3A. By wayof example, if the tube has an inner diameter of about 2 millimeters(0.002 meters) the surface area per meter length is calculated as about0.00628 square meters (pi×0.002 meter×1 meter) and water-swellablepowder or powder blends are mechanically attached to about 0.002 squaremeters or less of the surface area of the inner wall (i.e., aboutone-third of the surface area per meter).

Measurement of the amount of surface area having a water-swellablepowder or powder blend mechanically attached to a wall is measured bytaking an average of several regions of interest (i.e., sample areas)such as five one square millimeter regions of interest spaced along thetube and magnifying the same using a microscope and determining anaverage of the five sample areas. Specifically, each one squaremillimeter sample area is magnified 50× and examined using an imageanalysis software package such as I-Solutions software available fromImage and Microscope Technology of Vancouver, British Columbia Canada.FIG. 5 is a photograph showing a magnified view (about 50×) of the innerwall of a tube having powder mechanically attached thereto viewed usingthe I-Solutions software after any loose water-swellable powder orpowder blend has been removed. Specifically, a sample length of about100 millimeters long is cut and the optical fibers are removed from afirst end of the tube. Thereafter, the second end of the sample is slitabout 10-15 millimeters, thereby splitting a portion of sample in half.Next, any loose powder is removed from the sample by tapping the secondend (i.e., the split end) of the tube at least three times while holdingthe same in nearly vertical position so that any loose powder falls outof the sample. Finally, a portion of the split end is removed from thesample for viewing under magnification. FIG. 5 shows a region ofinterest 150 superimposed on a portion of the same that is depicted by aboxed area (i.e., the area within the dashed box is the region ofinterest).

FIG. 5 a is the same photograph shown in FIG. 5 with the powder withinthe region of interest 150 identified using the software to determinethe percentage of surface area within region of interest 150 that ismechanically attached thereto. In other words, the software allows themeasurement of the percentage of surface area having powder mechanicallyattached thereto since the gray scale differentiation reveals thesurface area having powder mechanically attached thereto relative to thetube wall. When using the software to determine the percentage ofsurface area having mechanical attachment, the threshold lighting shouldbe properly adjusted to view the contrast between areas. Specifically,the incident angle of the lighting should provide suitabledifferentiation and oversaturation of light should be avoided so thatthe contrast between areas is easily visible. Region of interest 150shown in FIG. 5 a has the powder mechanically attached to about 30percent or less of the region of interest 150 as depicted. In otherembodiments, the powder can be mechanically attached to 25 percent orless of the surface area. Further, from the image the size and shape ofthe powder is observable.

Besides the surface area of the tube or cavity having a given percentageof mechanical attachment, the total percentage of water-swellable powderor powder blend that is mechanically attached to the fiber opticassembly can be quantified. Illustratively, the water-swellable powderor powder blend 104 has a relatively high level (i.e., 45 percent ormore) of the same by weight mechanically attached to the inner tube walland the remaining 55 percent of the powder or powder blend is looselydisposed within the tube. By way of example, if fiber optic assembly has0.10 grams of powder per meter length, then about 0.045 grams or more ofthe powder is mechanically attached per meter length of the fiber opticassembly and 0.055 grams or less per meter is loose. Of course, thetotal percentage of the powder by weight mechanically attached can haveother values such as 50 percent or more, 55 percent or more, 60 percentor more, 75 percent or more, 80 percent or more, 90 percent or more, or95 percent or more, thereby respectively leaving 40 percent or more, 20percent or more, 10 percent or more, or 5 percent or more of the powderloosely disposed within the tube or cavity. Table 1 below shows theabove examples of total percentages of powder mechanically attached intabular form for a concentration level of 0.10 grams of powder per meterlength, but values for other concentration levels are also possible.

TABLE 1 Examples of Total Percentages of Powder Mechanically AttachedMechanically Attached Mechanically Powder by Weight Loose Powder byWeight Attached/Loose (%) (grams) (grams) 45/55 0.045 0.055 50/50 0.050.05 55/45 0.055 0.045 60/40 0.06 0.04 75/25 0.075 0.025 80/20 0.08 0.0290/10 0.09 0.01 95/10 0.095 0.005The total percentage of powder by weight mechanically attached can bedetermined by averaging the measured or calculated weight of themechanically attached powder per meter length divided by the totalweight of the powder per meter length disposed within the tube orcavity. Conversely, the total percentage of powder by weight looselydisposed can be determined by averaging the measured or calculatedweight of the loosely disposed powder per meter length divided by thetotal weight of the powder disposed within the tube or cavity. However,measuring the percentage of powder or powder blend that is mechanicallyattached is easier and more precise. Additionally, if one of thepercentages is known the other percentage may be calculated bysubtracting.

In further embodiments, fiber optic assemblies can also have relativelysmall average concentrations of powder per meter, thereby making thepowder in the fiber optic assembly nearly transparent to the craft. Forinstance, fiber optic assembly 100 may have about 0.02 grams of powderper meter length for a tube having a 2.0 millimeter inner diameter whilestill being suitable for blocking a one-meter pressure head of tap waterwithin a one meter length for twenty-four hours, but other suitableconcentration levels (i.e., weight per meter) both higher or lower arepossible. Additionally, the average concentration levels are scalablebased on cavity size.

By way of example, a cavity cross-sectional area for the 2.0 millimeterinner diameter tube is about 3.14 square millimeters, thereby yielding anormalized concentration value of about 0.01 grams of water-swellablepowder per meter length of the tube assembly when rounded up. In otherwords, the normalized concentration per square millimeter of cavitycross-sectional area is given by taking the average concentration suchas 0.02 grams per meter length of water-swellable powder divided by thecavity cross-sectional area of about 3 square millimeters to yield anormalized concentration value. In this example, normalizedconcentration value is about 0.01 grams of water-swellable powder persquare millimeter of the cavity cross-sectional area per meter length ofthe tube when rounded upward. Consequently, the average concentration ingrams per meter of water-swellable powder for cavities of tubes or fiberoptic cables having a given cross-sectional area can be scaled (i.e.,calculated) accordingly by using the normalized concentration value suchas of 0.01 grams of water-swellable powder per meter length for eachsquare millimeter of cavity cross-sectional area. Illustratively, if acavity cross-sectional area is five square millimeters and a normalizedconcentration value of 0.01 grams per meter length is desired, then thefiber optic assembly has a 0.05 grams of powder in the cavity per meterlength. In further embodiments, either higher or lower normalizedconcentration values are possible such as between 0.005 grams per meterlength and 0.02 grams per meter length. Generally speaking, as thecross-sectional area of the cavity of the tube or the like increases,the amount of water-swellable powder needed for effectively blocking themigration of water along the same may increase generally proportionatelyfor effective water-blocking.

The weight of the water-swellable powder per meter length (i.e., theconcentration per meter length) in the fiber optic assembly iscalculated by using the following procedure. A representative number ofsamples such as five one meter samples of the fiber optic tubeassemblies are cut from the assembly being tested. The samples arepreferably taken from different longitudinal portions along the fiberoptic assembly rather than serially cutting samples from the same. Eachone-meter sample is weighed with the optical fibers and water-swellablepowder in the tube for determining a total weight of the sample using asuitably precise and accurate scale. Thereafter, the optical fibers(along with any other removable cable components within the tube,cavity, or the like) are pulled from the tube. The optical fibers (andany other cable components) are wiped with a fine tissue to remove anywater-swellable powder thereon and then rinsed with water and wipedagain with a damp towel, dried, and then wiped with alcohol andthoroughly dried. Thereafter, the optical fibers (and other cablecomponents) are weighed to determine their weight without thewater-swellable powder. Next, the tube is optionally weighed (withoutthe optical fibers and other cable components) to determine its weightwith the powder therein for verification of results. Then the tube isopened up along its longitudinal length using a suitable tool and tappedat least three times so that the loose power falls out of the same andthen it is weight to determine the weight of the tube with themechanically attached particles. Thereafter, the remainingwater-swellable powder therein can be wiped from the tube rinsed withwater and wiped again with a damp towel, dried, and then wiped withalcohol and thoroughly dried taking care to make sure that nearly all ofpowder or powder blend is substantially removed, then the “cleaned” tubeis weighed to determine its weight without the water-swellable powder.Further, the optical fibers or portions of the tubes can be viewed undermagnification to determine if the powder has been suitably removedbefore weighing. Thereafter, the sum of the weight of the optical fiber(and other cable components) along with the weight of the tube issubtracted from the total weight for the sample to determine the weightof the water-swellable powder in the respective sample. This procedureis repeated for each of the representative number of samples. Theaverage concentration of water-swellable powder is calculated by addingall of the calculated weights of the water-swellable powders for thesamples and dividing by the number of samples, thereby arriving at anaverage concentration of the water-swellable powder per meter for thefiber optic assembly.

Even though optical fibers may contact the powder or powder blend, fiberoptic tube assemblies and/or cables such as fiber optic assembly 100preserve the optical performance of optical fibers 102 therein. Forinstance, the optical fiber(s) of the fiber optic tube assemblies have amaximum optical attenuation of about 0.15 db/km or less at a referencewavelength of 1550 nanometers during standard temperature cycling underGR-20, which cycles temperatures down to −40° C. For instance, typicalaverage optical attenuation values are about 0.05 db/km at a referencewavelength of 1550 nanometers during standard temperature cycling at−40° C. Furthermore, fiber optic tube assemblies have advantageouslybeen temperature cycled at a reference wavelength of 1550 nanometersdown to −60° C. using procedures similar to GR-20 while still having adelta attenuation of about 0.25 db/km or less without having to modifythe design.

One factor that can affect optical performance is the maximum particlesize, average particle and/or particle size distribution ofwater-swellable powder 104, which can impact microbending if the opticalfibers should contact (i.e., press against) the water-swellableparticles. Moreover, using water-swellable powders having relativelysmall particles improves the transparency of the same to the craft whenthe tube is opened. The average particle size for the water-swellablepowder is preferably about 150 microns or less, but other suitableaverage particles sizes are possible such as 60 microns or less. Theskilled artisan understands that since the powder is sieved using anappropriated sized mesh it has a distribution of particle sizes. Forinstance, individual particles may have an aspect ratio (i.e., longerthan wide) that still fit through the sieving mesh in one direction andare larger than the average particle size. Using SAPs with a somewhatlarger average maximum particle size may still provide acceptableperformance, but using a larger maximum particle size increases thelikelihood of experiencing increased levels of optical attenuation.Additionally, the shape of the particles may also affect the likelihoodof experiencing increased optical attenuation. In other words, particleshaving round surfaces are less likely to experience elevated levels ofoptical attenuation compared with particles having rough surfaces. Oneexplanatory water-swellable powder is a crosslinked sodium polyacrylateavailable from Evonik, Inc. of Greensboro, N.C. under the tradenameCabloc GR-211. The particle distribution for this explanatorywater-swellable powder is given by Table 2.

TABLE 2 Particle Distribution for an Explanatory Water-Swellable PowderParticle Size Approximate Percentage Greater than 63 microns 0.2% 45microns-63 microns 25.7% 25 microns-44 microns 28.2% Less than 25microns 45.9%

Of course, other powders, powder blends, and/or other particledistributions are possible. Another suitable crosslinked sodiumpolyacrylate is available from Absorbent Technologies, Inc. under thetradename Aquakeep J550P, still other types of water-swellable materialsare also possible. By way of example, another suitable water-swellablepowder is a copolymer of acrylate and polyacrylamide, which is effectivewith saline solutions. Furthermore, powder blends of two or morematerials and/or water-swellable powders are possible such as blend of aslow-swelling water swellable powder and a fast-swelling water swellablepowder. Likewise, a blend of water-swellable powder can include a firstwater-swellable powder that is highly-effective for a saline solutionand a second water-swellable powder effective for tap water. Powderblends may also include components that are not inherentlywater-swellable. By way of example, small amounts of silica such as afumed silica up to 3% may be added to a water-swellable powder forimproving flow properties and/or inhibiting anti-caking due to moistureabsorption. Additionally, concepts of the invention allow the use ofother types of particles with or without the water-swellable particlessuch as flame-retardant particles (e.g., aluminum trihydrate, magnesiumhydroxide, etc.), a dry lubricant like talc, graphite, boron, and/or thelike.

A further factor to consider when selecting a water-swellable materialis its absorption capacity. Absorption capacity is the amount of waterthat a unit of water-swellable material can absorb and is typicallymeasured in grams of water absorbed per gram of water-swellablematerial. In one embodiment, the water-swellable material preferably hasan absorption capacity of at least about 100 grams per grams ofwater-swellable material, but other values lower or higher are possible.For instance, the water-swellable material can have an absorptioncapacity of about 200 grams or more per gram of material, 300 grams ormore per gram of material, or 400 grams or more per gram of material.Several factors may affect a material absorption capacity such as thetype of material, the degree of cross-linking, the surface area, etc.

Another factor that may affect optical performance is excess fiberlength (EFL) or excess ribbon length (ERL). As used herein, excess fiberlength may refer to either EFL or ERL, but generally speaking ERL merelyrefers to excess ribbon length. Fiber optic assemblies of the presentinvention such as shown in FIG. 3 preferably have an excess fiber lengththat is preferably in the range of about −0.1% to about 0.3% to createacceptable contraction and tensile windows depending on the tube innerdiameter, but other suitable values of excess fiber length or excessribbon length are possible especially with other configurations/designsof fiber optic assemblies.

Furthermore, the powder or powder blends can inhibit the stickingbetween the optical fibers and the tube without using a separation layeror other material. Specifically, fiber optic assemblies can have issueswith the optical fibers contacting and sticking to the tube while it ismolten state when being extruded about the optical fibers. If theoptical fiber sticks to the inside of the tube it can cause the path ofthe optical fibers to be distorted (i.e., the optical fiber is preventedfrom moving at that point), which may induce undesirable levels ofoptical attenuation. As depicted in FIGS. 3 and 4, tube 106 is disposedabout optical fibers 102 of fiber optic assembly 100 without using afurther material or component as a separation layer (e.g., no gel,grease, yarn, tape, etc.) for inhibiting contact between the opticalfibers and the molten tube. Sticking is inhibited because thewater-swellable powder is a cross-linked material so it does not promotesticking thereto at typical extrusion temperatures. Thus,water-swellable powder 104 tends to act as a separation layer since itinhibits optical fibers 102 from sticking to the molten tube duringmanufacture. However, other cable components may be included within thetube or cavity.

Moreover, the water-swellable powder 104 acts to reduce the frictionbetween the optical fibers and the tube or cavity wall by acting as aslip layer. Simply stated, the particles of the water-swellable powder104 act like ball-bearings between the optical fibers 102 and the innerwall of the tube for reducing the friction therebetween and allowing theoptical fibers to move to a “relaxed state”. In other variations,embodiments of the present invention may optionally use a lubricant inor on the outer layer of the optical fibers, thereby reducing the riskof optical fibers sticking to the extruded tube and/or reducing thefriction therebetween. For instance, optical fibers 102 may include anouter layer such as an ink having a suitable lubricant for inhibitingoptical fibers 102 from sticking to the molten tube 106 during extrusionof the same. Suitable lubricants include silicone oil, talc, silica orthe like used in a suitable amount that it will inhibit “caking-up” andis disposed in or on the outer layer. Other methods are also availablefor inhibiting the sticking of optical fibers with the tube. Forinstance, tube 106 may include one or more suitable fillers in thepolymer, thereby inhibiting the adherence of the optical fibers with thetube. Additionally, the use of other polymer materials for the tube suchas a highly-filled PVC can inhibit sticking of the optical fibers to thetube. Furthermore, tube 106 may have a dual-layer construction with aninner layer of the tube having one or more suitable fillers in thepolymer for inhibiting adhesion. Another way for inhibiting sticking ofthe optical fibers is to apply a lubricant to the inner wall of the tubeor cavity shortly after forming the same.

Tube 106 may use any suitable polymer material for housing andprotecting the optical fibers 102 therein. For instance, tube 106 can bea polypropylene (PP), polyethylene (PE), or blends of materials such asa blend of PE and ethylene vinyl acetate (EVA). In other embodiments,tube 106 is formed from a flame-retardant material such asflame-retardant polyethylene, flame-retardant polypropylene, polyvinylchloride (PVC), or polyvinylidene fluoride PVDF, thereby forming aportion of a flame retardant fiber optic cable. However, tube 106 neednot necessarily be formed from a flame-retardant material for making aflame-retardant fiber optic cable. In still other embodiments, tube 106may comprise a thin sheath that is easily tearable by the craft withouttools. For instance, tube 106 is formed from a highly filled material,thereby making it is easily tearable by the craftsman merely using theirfingers to tear the same. By way of example, tubes that are easilytearable may include a filled materials such as polybutyleneterephthalate (PBT), a polycarbonate and/or a polyethylene (PE) materialand/or an ethylene vinyl acrylate (EVA) or other blends thereof havingfillers like a chalk, talc, or the like; however, other suitablematerials are possible such as a UV-curable acrylates. Generallyspeaking, all other things being equal tube 106 can have a smaller innerdiameter ID compared with dry tube assemblies that include awater-swellable yarn, tape, or thread (i.e., a carrier for the SAP) withthe optical fibers. This is because tube 106 does not have to providethe space for both the optical fibers and the carrier of the SAP (i.e.,the yarn(s) or tapes); consequently the inner diameter ID may besmaller. For instance, having a smaller inner diameter ID for tube 106is also advantageous since it allows for a smaller outer diameter, amore flexible assembly having a smaller bend radius (which may reducekinking), is lighter in weight per length, and can fit longer lengths ona reel.

Illustratively, twelve standard sized 250 micron optical fibers arrangedin a bundle having an overall diameter of about 1.2 millimeters can behoused in a tube or cavity with the inner diameter ID such as about 1.7millimeters or less such as 1.6 millimeters or even as small as 1.5millimeters or 1.4 millimeters with suitable performance down to −40° C.Other suitable inner diameters ID for the tube are possible and the IDcan depend on the number of optical fibers within the tube or cavity. Byway of comparison, a conventional fiber optic assembly with twelveoptical fibers and a plurality of water-swellable yarns requires aninner diameter of about 2.0 millimeters to accommodate both thewater-swellable yarns and the optical fibers.

Mechanical attachment of the water-swellable particles or powder blend104 may be created by any suitable manufacturing process. One way ofcreating the mechanical attachment is to provide the particles of thepowder with a suitable momentum so they impact a cone of a moltenpolymer that forms tube 106 as it is exiting the extruder. When theinner surface of tube 106 is still molten, at least some of theparticles of powder are mechanically attached and/or transferred theretowhen provided with a suitable momentum. Generally speaking, the suitablemomentum can be effectuated by applying forces for imparting a velocityto the particles such as by air injection and/or by electrostaticcharge. By way of example, powder having an average particle size of 60microns or less can be directed to the molten tube with an exit velocityof about 20 meters/second for creating mechanical attachment thereto.

FIG. 6 is a cross-sectional view of a fiber optic cable 60 using severalfiber optic assemblies 100 according to the present invention. Asdepicted, fiber optic assemblies 100 are stranded about a central member61 along with a plurality of filler rods 62 and a plurality of tensilestrength yarns 63, which have a water-swellable tape 65 disposedthereabout, thereby forming a fiber optic cable core (not numbered).Fiber optic cable 60 also includes a cable jacket disposed about thecable core for protecting the same. Any suitable strength elements arepossible for tensile strength yarns 63 such as aramid yarns, fiberglass,or the like. Fiber optic cable 60 may also include other components suchas one or more water-swellable yarns or a water-swellable tape disposedabout central member 61. Additionally, fiber optic cable can eliminateelements such as the central member or other cable components if notnecessary. Cable jacket 68 of fiber optic cables 60 a and 60 b may useany suitable material such as a polymer for providing environmentalprotection.

In one embodiment, cable jacket 68 is formed from a flame-retardantmaterial, thereby making the fiber optic cable flame retardant.Likewise, tube 106 of fiber optic assembly 100 may also be formed from aflame-retardant material, but using a flame-retardant for the tube maynot be necessary for making a flame-retardant cable. By way of example,a flame-retardant fiber optic cable may include cable jacket 68 formedfrom a polyvinylidene fluoride (PVDF) and tube 106 formed from apolyvinyl chloride (PVC). Of course, the use of other flame retardantmaterials is possible such as flame-retardant polyethylene orflame-retardant polypropylene.

FIG. 7 is a cross-sectional view of a fiber optic cable 70 that issimilar to fiber optic cable 60, but it further includes an armor layer77. Like fiber optic cable 60, fiber optic cable 70 includes a pluralityof fiber optic assemblies 100 stranded about a central member 71 alongwith a plurality of filler rods 72 and a water-swellable tape 75,thereby forming a cable core (not numbered). Armor layer 77 is disposedabout water-swellable tape 75 and as shown formed from a metallicmaterial, but other suitable materials may be used for the armor such asa polymer. Fiber optic cable 70 also includes a cable jacket 78 disposedabout armor layer 77.

FIG. 8 is a cross-sectional view of another fiber optic cable 80configured as a monotube fiber optic cable design. More specifically,fiber optic cable 80 includes a single fiber optic assembly (notnumbered) similar to fiber optic assembly 100 with optical fibers 102and water-swellable powder 104 within tube 106, but it further includesa plurality of optional coupling elements 81 for providing a couplingforce to optical fibers 102. Since this is a monotube design coupling isnot provided by stranding of the fiber optic assemblies like fiber opticcables 60 and 70. Coupling elements 81 can be any suitable constructionand/or material such as a string, thread, yarn, tape, elastomer element,or the like that can be wrapped about the optical fiber(s) orlongitudinally disposed in the tube or cavity. Other variations forcreating coupling include a surface roughness on the inner surface ofthe tube or cavity or extruding a material on the optical fibers such asan elastomer, fugitive glue or the like. As desired other embodimentsmay include any other suitable coupling element(s). Fiber optic cable 80also includes a plurality of strength members 88 such as tensile yarnsdisposed radially outward of tube 106, but other types of strengthmembers are possible such as GRPs. A cable jacket 88 is disposed aboutstrength members 88 for providing environmental protection.

Although, the previous embodiments depict the fiber optic assembly orfiber optic cable as being round it can have other shapes and/or includeother components. For instance, FIG. 9 is a cross-sectional view of afiber optic cable 90 according to the present invention. Fiber opticcable 90 includes optical fibers 102 and water-swellable powder 104within a cavity 96 of cable jacket 98, which essentially is a tube forthe fiber optic assembly. In this embodiment, cable jacket 98 isnon-round and forms the cavity 96 for housing optical fibers 102 andwater-swellable powder 104. Simply stated, fiber optic cable 90 is atubeless configuration since optical fibers 102 can be accessed oncecable jacket 98 is opened. In other words, the fiber optic cable doesnot include a buffer tube, but instead cable jacket 98 is the tube.Moreover, tube 98 (i.e., cable jacket) includes strength member 97disposed therein (i.e., encapsulated within the cable jacket) and onopposite sides of cavity 96, thereby forming a strengthened tube orcable sheath. Of course, cavity 96 could have other shapes such asgenerally rectangular to generally conform to the shape of one or morefiber optic ribbons.

FIG. 9 and similar fiber optic cables that are tubeless, per se, can bemanufactured by elastically straining the strength members while thecable jacket is being extruded thereover for creating and/or controllingthe excess fiber length/excess ribbon length (EFL/ERL). Fiber opticcable 90 has a generally flat shape, but the concepts of elasticallystretching the strength members are suitable with any suitablecross-sectional shape for the cable such as round. Specifically,strength members 97 are paying-off respective reels under a relativelyhigh tension (e.g. between about 100 to about 400 pounds) usingrespective strength member capstans, thereby elastically stretchingstrength members 97 so that excess fiber length EFL (or ERL) is producedin fiber optic cable 90. In other words, after the tension is releasedon strength members 97 they return to their original unstressed length(i.e. shorten), thereby producing EFL since the optical fibers wereintroduced into the fiber optic cable with about the same length astensioned strength members and the optical fibers were not stretched.Stated another way, the amount of EFL produced is equal to about thestrength member strain (i.e., elastically stretching of the strengthmember) plus any plastic shrinkage of the cable jacket that may occur.The strength member strain can create a significant amount of EFL or ERLin a one-pass production such as 10% or more, 25% or more, 50% or more,and even up to 80% or more of the total EFL or ERL within the cable.Furthermore, elastically stretching of the strength member isadvantageous since it allows for a precise control of the amount of EFLor ERL being introduced into the cable and greatly reduces strengthmember pistoning since the finished cable jacket is in compressioninstead of tension. For the manufacture of fiber optic cable 90, about95% of EFL is introduced into the cable by elastically stretching thestrength members. Simply stated, the cable jacket (i.e., the tube) isbeing applied about the optical fibers, water-swellable powder andstrength members by a cross-head extruder while strength members 97 areelastically stretched. After extrusion, cable 90 is then quenched inwater trough while the strength member is still elastically stretched,thereby allowing the cable jacket to “freeze” on the stretched strengthmembers. The fiber optic cable 90 is then pulled through themanufacturing line using one or more caterpullers and then wound ontotake-up reel under low tension (i.e., the tensile force that elasticallystretched the strength members is released and strength members returnto a relaxed length thereby creating ERL or EFL in the cable). Ofcourse, this is merely an explanatory manufacturing line and othermodifications are possible.

FIG. 10 depicts a cross-sectional view of a fiber optic cable 110 havinga main cable body 101 and a tonable lobe 103. Fiber optic cable 110includes a fiber optic assembly 100 having optical fibers 102 andwater-swellable powder 104 within tube 106. Fiber optic cable 110 mayalso include one or more water-swellable yarns (not visible) or awater-swellable tape disposed about tube 106 for blocking the migrationof water along the fiber optic cable outside fiber optic assembly 100.Fiber optic cable 110 also includes a plurality of strength members 107such as GRPs disposed on opposite sides of tube 106. Although strengthmembers 107 are shown slightly spaced apart from tube 106 they maycontact the same. Moreover, other materials are possible for strengthmembers 107 such as steel wires or other suitable components. Fiberoptic cable 110 also includes a cable jacket 108 formed from a suitablepolymer, which forms a portion of main cable body 101 and tonable lobe103 as shown. Tonable lobe 103 includes a toning wire 103 a that is asuitable conductive element such as a copper wire or copper clad steelwire suitable for sending a signal for locating fiber optic cable 110when buried. By way of example, toning wire 103 a is a 24 AWG gaugecopper wire. Additionally, toning lobe 103 has a frangible web (notnumbered) for separating the same from the main cable body 101 whendesired such as before connectorization. Of course, other variations arepossible.

FIG. 11 depicts a cross-sectional view of a fiber optic cable 120 thatis a tubeless configuration (i.e., the cable jacket acts as the tube)having a plurality of fiber optic ribbons 122 therein as represented bythe horizontal lines. Although fiber optic cable 120 is shown as agenerally flat cable design it could have other suitable shapes such asvariations of a flat cable or a round cable. As discussed above, themanufacture of fiber optic cable 120 is similar to the manufacture offiber optic cable of FIG. 9. Fiber optic ribbons include a plurality ofoptical fibers (not visible) attached together using a suitable matrixmaterial such as a UV curable matrix. Specifically, fiber optic cable120 includes four fiber optic ribbons 122 each having twenty-fouroptical fibers for a total of ninety-six optical fibers, thereby forminga ribbon stack (not numbered). Similar fiber optic cables can have otherfiber-counts within the ribbon and/or the fiber optic cable. Asdescribed above, fiber optic cable 120 includes water-swellable powder104 that is at least partially mechanically attached on the innersurface of a cavity 126 of a cable jacket 128 and/or disposed on thefiber optic ribbon(s). For instance, powder or powder blend 104 has anormalized concentration of about 0.01 grams or less per meter for eachsquare millimeter of cavity 126 of the fiber optic assembly, but othersuitable concentrations may be used. By way of example, cavity 126 issized to receive fiber optic ribbons (i.e., fiber optic components) andhas a cavity width measured in millimeters and a cavity height measuredin millimeters, which are multiplied together to calculate a cavitycross-sectional area in square millimeters. The stack of fiber opticribbons also has a total cross-sectional area measured in squaremillimeters. The average concentration of water-swellable powder may becalculated using the cavity cross-sectional area or an effective cavitycross-sectional area. The effective cavity cross-sectional area isdefined as the cavity cross-sectional area minus the cross-sectionalarea of the desired components therein such as the fiber optic ribbonswithin the cavity. Illustratively, an effective cross-sectional iscalculated by subtracting the cross-sectional area of the fiber opticribbons from the cavity cross-sectional area, which yields an effectivecavity cross-sectional area in square millimeters. Thus, an averageconcentration for the amount of water-swellable powder in this design iscalculated by taking the desired normalized concentration (grams permeter length of the assembly per square millimeter of the cavity) timesthe effective cavity cross-sectional area (square millimeters), whichyields an average concentration for the water-swellable powder in gramsper meter length of the assembly.

Additionally, fiber optic cable 120 may optionally include one or morecoupling elements 121 as shown in phantom lines. When including one ormore coupling elements 121 less of water-swellable powder 104 may betransferred to an inner surface of cavity 126 since the couplingelements 121 can inhibit the transfer (i.e., they are between a portionof the fiber optic ribbons and the cavity walls). More specifically,fiber optic cable 120 has two coupling elements (represented by theshaded rectangles) formed from a longitudinal foam tape, or othersuitable coupling element disposed on opposite sides of the ribbon stackso that the coupling elements 121 sandwich the fiber optic ribbons 122therebetween. Below is representative example to determine the averageconcentration of water-swellable powder using the effective cavitycross-sectional area for a larger cavity having fiber optic ribbons andcoupling elements therein. In this instance, cavity 126 is sized toreceive four twenty-four fiber optic ribbons (i.e., fiber opticcomponents) and has a cavity width of about 8.2 millimeters and a cavityheight of 5.2 millimeters, which are multiplied together to calculate acavity cross-sectional area of about 43 square millimeters. The stack offiber optic ribbons also have a total cross-sectional area of about 7.4square millimeters and the sum of the coupling elements have across-sectional area of about 27.2 square millimeters. Thus, theeffective cross-sectional for this example is calculated by subtractingthe cross-sectional area of the fiber optic ribbons and couplingelements from the cavity cross-sectional area (i.e., 43 mm²-7.4 mm²-27.2mm²), which yields an effective cavity cross-sectional area of about 8square millimeters. Thus, an average concentration for the amount ofwater-swellable powder for this design is calculated by taking thedesired the normalized concentration times the effective cavitycross-section (i.e., 0.01 grams per meter length per square millimetertimes 8 square millimeters), which yields an average concentration ofabout 0.08 grams per meter length for the cavity of the example thathouses 96-optical fibers in a ribbon stack. Although, the averageconcentration of water-swellable powder is larger it still is a traceamount for water-blocking a larger effective cavity cross-sectionalarea, which is hardly noticeable by the craft and still effectivelyblocks the migration of water along the cavity of the fiber optic cable.Of course, other examples according to these concepts of the inventionare possible.

Additionally, coupling elements 121 provide the optical fibers for thisdesign with a coupling force of at least about 0.1625 Newtons peroptical fiber for a thirty-meter length of fiber optic cable providedone or more coupling elements 121. Illustratively, a fiber optic cablehaving a single ribbon with twelve optical fibers in the ribbon shouldhave a coupling force of about 1.95 Newtons or greater for athirty-meter length of fiber optic cable. Likewise, a similar fiberoptical cable having a single optical fiber ribbon with four opticalfibers should have a coupling force of about 0.650 Newtons or greaterfor a thirty-meter length of fiber optic cable. Measurement of thecoupling force is accomplished by taking a thirty-meter fiber opticcable sample and pulling on a first end of the optical fibers (or fiberoptic ribbon(s)) and measuring the force required to cause movement ofthe second end of the optical fiber(s) (or fiber optic ribbon(s)). Inother words, the excess fiber length (EFL), or excess ribbon length(ERL), must be straightened so that the coupling force is the amount offorce required to move the entire length of optical fibers within thethirty-meter fiber optic cable sample. Besides providing coupling,coupling elements 121 can also cushion the ribbon stack, while stillallowing movement of the fiber optic ribbons.

Fiber optic ribbons 122 of this design generally have more ERL than tubedesigns since the ribbon stack is not stranded. By way of example, fiberoptic ribbons 122 have an ERL in the range of about 0.1% to about 1.2%or more and the amount of ERL can depend on the number of fiber opticribbons within the stack and the strength members would be elasticallystretched in a range similar to the desired ERL. Moreover, fiber opticcable 120 can use a manufacturing process similar to that described withrespect to fiber optic cable 90 to elastically stretch one or morestrength members 127, thereby creating the ERL. Specifically, a firststrength member 127 and a second strength member 127 that are disposedon opposite sides of cavity 126 are elastically stretched by apredetermined amount during the extrusion of cable jacket 128.Furthermore, fiber optic cable 120 can be a portion of a distributionfiber optic assembly having one or more optical fibers split out fordistribution. The optical fibers split out for distribution can bespliced with a tether, attached to a ferrule/connector, or merely beleft splice ready for the craft.

Many modifications and other embodiments of the present invention,within the scope of the claims will be apparent to those skilled in theart. For instance, the concepts of the present invention can be usedwith any suitable fiber optic cable design and/or method of manufacture.For instance, the embodiments shown can include other suitable cablecomponents such as an armor layer, coupling elements, differentcross-sectional shapes, or the like. Thus, it is intended that thisinvention covers these modifications and embodiments as well those alsoapparent to those skilled in the art.

We claim:
 1. A fiber optic cable, comprising: a tube, the tube having aninner wall defining a cavity; an optical fiber disposed in the cavity ofthe tube; water-swellable powder, wherein at least a portion of thewater-swellable powder is mechanically attached to a surface of thecavity, wherein the mechanical attachment of the water-swellable powderallows a portion of particles of the water-swellable powder to protrudebeyond the surface and not be completely embedded therein, wherein theaverage particle size for the water-swellable powder is about 150microns or less, thereby reducing impact of microbending if the opticalfiber should contact the particles of the water-swellable powder.
 2. Thefiber optic cable of claim 1, wherein the particles of thewater-swellable powder have round surfaces, whereby the optical fiber isless likely to experience elevated levels of optical attenuation.
 3. Thefiber optic cable of claim 1, wherein the optical fiber has a maximumoptical attenuation of about 0.15 dB/km or less at a referencewavelength of 1550 nanometers during standard temperature cycling underGR-20, which cycles temperatures down to −40° C.
 4. The fiber opticcable of claim 1, wherein the water-swellable powder has an absorptioncapacity of at least about 100 grams per grams of water-swellablepowder.
 5. The fiber optic cable of claim 1, wherein the mechanicalattachment of the water-swellable powder is uniformly disposed on thesurface of the cavity.
 6. The fiber optic cable of claim 5, wherein themechanical attachment of the water-swellable powder covers 30 percent orless of the entire surface of the cavity.
 7. The fiber optic cable ofclaim 1, wherein the water-swellable powder has 45 percent or more ofthe same by weight mechanically attached to the surface of the cavity.8. The fiber optic cable of claim 1, wherein the tube comprises at leastone of polypropylene, polyethylene, polyvinyl chloride, orpolyvinylidene fluoride.
 9. The fiber optic cable of claim 8, whereinthe tube comprises a flame-retardant material.
 10. The fiber optic cableof claim 1, wherein the cavity has an inner diameter of about 1.7millimeters or less.
 11. The fiber optic cable of claim 1, wherein thetube is a cable jacket, and wherein the cable jacket is non-round. 12.The fiber optic cable of claim 11, wherein the cavity has a rectangularshape.
 13. A cable for optical fibers, comprising: a tube, the tubehaving an inner wall defining a cavity; water-swellable powder, whereinat least a portion of the water-swellable powder is mechanicallyattached to a surface of the cavity, wherein the mechanical attachmentof the water-swellable powder allows a portion of particles of thewater-swellable powder to protrude beyond the surface and not becompletely embedded therein, wherein the water-swellable powder has anabsorption capacity of at least about 100 grams per grams ofwater-swellable powder.
 14. The fiber optic cable of claim 13, whereinthe particles of the water-swellable powder have round surfaces.
 15. Thefiber optic cable of claim 13, wherein the mechanical attachment of thewater-swellable powder is uniformly disposed on the surface of thecavity covering 30 percent or less of the entire surface.
 16. The fiberoptic cable of claim 13, wherein the water-swellable powder has 45percent or more of the same by weight mechanically attached to the innertube wall.
 17. A fiber optic cable, comprising: a tube, the tube havingan inner wall defining a cavity; an optical fiber disposed in the cavityof the tube; water-swellable powder, wherein at least a portion of thewater-swellable powder is mechanically attached to a surface of thecavity, wherein the water-swellable powder has 45 percent or more of thesame by weight mechanically attached to the inner tube wall, and whereinthe mechanical attachment of the water-swellable powder allows a portionof particles of the water-swellable powder to protrude beyond thesurface and not be completely embedded therein.
 18. The fiber opticcable of claim 17, wherein the particles of the water-swellable powderhave round surfaces, whereby the optical fiber is less likely toexperience elevated levels of optical attenuation.
 19. The fiber opticcable of claim 17, wherein the optical fiber has a maximum opticalattenuation of about 0.15 dB/km or less at a reference wavelength of1550 nanometers during standard temperature cycling under GR-20, whichcycles temperatures down to −40° C.
 20. The fiber optic cable of claim17, wherein the mechanical attachment of the water-swellable powder isuniformly disposed on the surface of the cavity covering 30 percent orless of the entire surface.